1. Field of the Invention
The present invention relates to a feedthrough assembly for conducting an optical fiber into the interior of a package for an opto-electronic device and, in particular, to such a feedthrough assembly having a rigidizing arrangement therein.
2. Description of the Prior Art
Opto-electronic communications systems which utilize light energy to transmit intelligence between a transmitting device and a receiving device are known. Exemplary of such systems are those shown in U.S. Pats. Nos. 4,119,363 (Camlibel et al.); 4,615,031 (Eales et al.); 4,482,201 (Dousset); 4,456,334 (Henry et al.); 4,360,965 (Fujiwara); and 4,338,577 (Sato et al.); United Kingdom Pats. Nos. 2,131,971 (Plessey) and 2,124,402 (Standard Telephone and Cables) and EPO Application No. 181,532 (Siemens).
Such communications systems typically include a transmitting device utilizing a light source, such as a solid state laser, and a receiving device utilizing a photoresponsive semiconductor. The functional elements of both the transmitting device and the receiving device are housed in a hermetically sealed package having a stability leak rate equal to or less than 1.times.10.sup.-8 atmospheres cc/sec Helium.
The light signals utilized in such systems are conveyed between the transmitting and receiving devices over an optical fiber link. United Kingdom Pats. Nos. 1,585,899 (Plessey) and 2,150,858 (Standard Telephone and Cable) disclose typical examples of optical fibers useful for this purpose. U.S. Pat. No. 4,565,558 (Keil et al.) and German Application No. 3,407,820 (Siemens) both relate to techniques whereby an optical fiber may be provided with a lensed end whereby light energy may be effectively coupled thereinto.
The fiber is usually supported in a feedthrough assembly comprising a metal sleeve surrounding the fiber. The fiber is stripped of its protective jacket for a predetermined distance adjacent its lensed end. The sleeve is crimped or otherwise fastened into secure contact with the jacket. The lensed end of the optical fiber may project past the end of the metal sleeve. The annular region between the inner surface of the sleeve and the exposed outer surface of the fiber is hermetically sealed, as by a glass insert. U.K. Pat. No. 1,541,495 (standard Telephone and Cable) and U.S. Pats. Nos. 4,430,376 (Box) and 4,566,892 (Ertel) all disclose glass to metal seals. Copending application Ser. No. 074,791, filed contemporaneously herewith, claiming priority from U.K. Application No. 8629158 filed Dec. 5, 1986, discloses a feedthrough assembly for an optical fiber having a glass insert that forms a hermetic seal between the fiber and the sleeve. In accordance with this last referenced application all of the stresses on the insert are compressive in nature in order to minimize the tendency of cracking to occur or to propagate.
Each package is provided with an aperture whereby the feedthrough assembly may enter into the interior thereof. The feedthrough assembly is appropriately positioned with respect to the package in a suitable relationship with the functional element of the transmitting or receiving device, as the case may be, and thereafter secured, as by laser welding, so as to remain in that selected position. United Kingdom Application Serial No. 8708032, filed Apr. 3, 1986, discloses a laser welding method whereby the feedthrough may be secured in the package.
When a situation is presented in which the fiber is attached adjacent one end of its sleeve by a hermetic seal, however formed, and the jacket of the fiber is also attached to the sleeve, as by crimping, there occurs a phenomenon known as "grow out". Grow out is the tendency of the jacket to grow and to contract axially relative to the fiber under thermal cycling so that the portion of the glass fiber intermediate these points of attachment undergoes compressive axial loading which leads to column bending. The bending may be of such a magnitude that the fiber fractures and is thus unable to conduct light energy. It should be understood that the tendency to grow out would occur whatever the form of the hermetic seal and whatever the form of attachment between the jacket and the sleeve. It is known in the art to protect and to support the fiber in the region between these points of attachment with an epoxy material, as disclosed in the above-cited patent to Eales et al. By introducing the epoxy into the region between these points of attachment both the fiber and its jacket may be attached to a common support member thereby mitigating the effects of grow out. Because of the small dimensions and close tolerances involved the epoxy is commonly introduced using a vacuum backfill process. It is also known in the art to use epoxy glass tubes for forming an optical splice. Exemplary of such a system is the UVC Optical Splice and the Splice for Pigtails (P/N 20126), both sold by Norland Products Inc., New Brunswick, N.J.
In view of the foregoing it is believed advantageous to provide an optical fiber feedthrough assembly that reduces the effects of grow out while avoiding a vacuum backfill process.